Filters for continuous filtering of a suspension are common within e.g. cellulose industry where suspensions have large volume flow and have comparatively high concentration of solid phase. The type of filter, up to now, most commonly existing for this purpose is rotating drum or disc filters which operate with vacuum for establishing required difference pressure over the filter.
Filters of said type have certain obvious disadvantages. In order to establish vacuum it is common, particularly where the hydraulic flow is large, to arrange a so called barometric fallpipe having a vertical length of 6-10 m. This, means that to establish the fallpipe height, the filter must be positioned at such a height, that increasing building and pump costs often result. Alternatively, a vacuum pump can be used; however, the power requirement and thereby the operation costs become high. Another disadvantage when using a vacuum filter is the dependence of the temperature for causing required high vacuum. At higher temperature, the lower vacuum is possible. At temperature over 90.degree. C. it is no longer possible to establish required vacuum and difference pressure. But also at moderate and low temperatures yielding the conditions for a high vacuum, the theoretically maximum pressure can never exceed 100 kPa.